Teamを右クリック → System console → Service Settings 以下の項目をTrueにする
Enable Incoming Webhooks: true
When true, incoming webhooks will be allowed. To help combat phishing attacks, all posts from webhooks will be labelled by a BOT tag.
Enable Outgoing Webhooks: true
When true, outgoing webhooks will be allowed.
Enable Slash Commands: true
When true, user created slash commands will be allowed.
Enable Integrations for Admin Only: true
When true, user created integrations can only be created by admins.
Enable Overriding Usernames from Webhooks and Slash Commands: true
When true, webhooks and slash commands will be allowed to change the username they are posting as. Note, combined with allowing icon overriding, this could open users up to phishing attacks.
Enable Overriding Icon from Webhooks and Slash Commands: true